1. Field of the Invention
The present invention relates generally to a precoder and a precoding method in a multi-antenna system. More particularly, the present invention relates to a precoder and a precoding method for canceling interference of multiple terminals in a multiuser multi-antenna system.
2. Description of the Related Art
As a result of the rapid growth of the wireless mobile communication industry and the increasing demand for the provision of various multimedia services in a wireless environment, there is an increasing need for communication systems capable of transmitting large amounts of data at a high data rate. In accordance with the need for the transmission of large amounts of data at a high data rate transmission for the provision of multimedia services, research is being conducted on a multi-antenna system (e.g., Multiple Input Multiple Output (MIMO) system) for efficiently utilizing limited frequency resources.
Compared to a single-antenna system, the multi-antenna system is able to increase transmission reliability and data rate by sending data over independent channels via antennas without allocating additional frequencies or transmit power. Moreover, the multi-antenna system can be extended to a multiuser multi-antenna system which supports a plurality of users.
The multiuser multi-antenna system can further increase the frequency efficiency such that multiple users can share the space resources acquired through the use of multiple antenna.
In the multiuser multi-antenna system, a transmitting end precodes and transmits data to prevent interference among the users.
For example, the transmitting end adopts a linear approach such as Zero Forcing (ZF) scheme, Minimum Mean Square Error (MMSE) scheme or a block diagonalization, to mitigate interference among the users.
In addition, the transmitting end adopts a nonlinear approach such as dirty paper coding or Tomlinson-Harashima precoding, to mitigate interference among the users.
If the ZF or the MMSE precoding is used to cancel interference among the users in the multiuser multi-antenna system, implementation of the transmitting end can be simplified. When the users' respective channels are not mutually orthogonal, however, the transmitting end suffers from enhancement of the transmitting signal power due to channel inversion.
If the multiuser multi-antenna system uses the dirty paper coding to cancel the interference among the users and the transmitting end accurately knows the users' channel information, channel capacity can be raised by canceling the interference among the users. Nevertheless, canceling the interference among the users using the dirty paper coding is considered to be impossible to implement due to the complexity of the transmitting end.
If the multiuser multi-antenna system uses the block diagonalization to cancel the interference among the users, however, the complexity of the transmitting end can be reduced, compared to the complexity of dirty paper coding, by allocating the next user to a null space of the channel of a specific user selected from the users to be serviced and sequentially canceling the interference. To achieve the maximum sum rate of block diagonalization, however, each user needs to know the decoding information obtained form the transmitting end. In order to do so, the transmitting end needs to send the decoding information to each user via coordinated information.
As discussed above, the transmitting end of the multiuser multi-antenna system transmits the signal using the precoding to mitigate the interference among the serviced users. When the transmitting end employs the linear interference cancellation scheme, however, its implementation can be simplified but results in performance degradation. When using the nonlinear interference cancellation scheme, performance is quite good but complexity increases.
Therefore, a novel precoding method is required for achieving a high level of performance while lowering the complexity of the multiuser multi-antenna system.